SACRAMENTO — Hoping to reduce the number of Californians who cycle in and out of prison, Gov. Arnold Schwarzenegger has quietly signed a bill allowing nonviolent ex-convicts to earn their way off parole early by completing an intensive drug treatment program.

The new law marks a significant -- and wise -- change in the state's approach to parole, says an expert who has previously accused the governor of wavering on prison reform. UC Irvine criminologist Joan Petersilia said other states have already demonstrated the benefit of giving low-risk ex-felons a chance to shorten their parole terms through good behavior.

"This is good policy because it adds a carrot to the stick we use so heavily in parole in this state," she said. "The research shows that if you give people incentives, they are more likely to stay involved in treatment and succeed."

Under the law, which takes effect in January, only ex-convicts who were serving time for nonviolent crimes -- such as drug or property offenses -- and have completed at least six months of addiction treatment in prison will be eligible. No one convicted of a sex offense will qualify.

Once released, eligible parolees who wish to participate will be sent directly to a residential drug treatment program for five months. If they graduate, they will immediately be freed from parole supervision.

By contrast, most California parolees now undergo three years of monitoring by their parole agent and are subject to conditions limiting travel and other aspects of their lives. A small number are discharged after one or two years, if they have no dirty drug tests or other violations.

The bill's author, state Sen. Jackie Speier (D-Hillsborough), said she was surprised but delighted that the Republican governor signed her measure, especially during an election year when a move shortening parole terms could be labeled soft on crime.

The bill enjoyed support from a wide variety of groups, including the politically powerful prison guards union. Lance Corcoran, a spokesman for the California Correctional Peace Officers Assn., said parolees "who demonstrate that level of commitment to treatment deserve recognition for their effort."

"It's a concept worth supporting," he said. "The only question is how they are going to come up with enough drug treatment beds for everybody who qualifies."

Administration officials said they would expand the inventory of treatment programs for inmates and parolees as quickly as possible, although there is no money specified by the bill.

Speier said she sponsored the measure in part because 75% of the state's 172,000 inmates have histories of drug or alcohol addiction. Of those released each year, 60% will return to prison within three years, she said.

"If we can help them conquer their addictions and get them off this treadmill of returning to prison, we'll save the taxpayers hundreds of millions of dollars," Speier said. The Department of Corrections and Rehabilitation spends more than $100 million a year on drug treatment programs inside prisons, she said, but much of it is wasted because many parolees do not undergo follow-up treatment and relapse.

Speier said the new law would save the state money by keeping some ex-convicts from returning to prison and by reducing parole supervision costs, which run $4,340 annually for each parolee. Savings would be offset somewhat by the creation of new drug treatment beds for inmates and parolees.

Schwarzenegger spokeswoman Margita Thompson said the law reflects the governor's focus on "protecting public safety and reducing the recidivism rates in California's prisons."

She said research shows that in-prison treatment, with after-care in the community, improves the odds that a parolee will break the cycle of addiction.

Thompson also said the governor has repeatedly voiced the desire to better prepare inmates for release and even added the word "rehabilitation" to the name of the Department of Corrections.

Petersilia, who has worked as a corrections consultant for the Schwarzenegger administration but has also criticized its prison reform efforts, praised the governor for signing the bill. She said it marked a "serious attempt by the administration to begin basing its corrections policy on science."

"Right now in California, we have this kind of vanilla approach to parole -- everybody gets it for about the same length of time and under the same conditions," Petersilia said. The new law "for the first time represents an effort to tailor parole to the risk posed by the offender."

She added that if allowing nonviolent parolees with drug addictions to earn their way off parole proves successful, the state should try the same approach with other low-risk ex-convicts. She said officials could offer early release from parole to someone who, for instance, holds a part-time job and has stable housing continuously for a year.